Method of manufacturing cores



I p 1969 A. v. HUGHES 3,466,744

METHOD OF MANUFACTURING CORES I I 2 Sheets-Sheet 1 Original Filed June 2, 1958 INVENTOR.

W I m v m 5 illlllll x min PM... w 7 n i u 1 I I 1 I p 6, 1969 A. v. HUGHES 3,466,744

METHOD OF MANUFACTURING CORES Original Filed June 2, 1958 2 Sheets-Sheet 2 INVENTOR.

United States Patent Int. Cl. H011 7/06 US. Cl. 29-606 Claims This application is a division of my application, Ser. No. 739,232, filed June 2, 1958, and now Patent No. 3,252,118.

This invention relates to a method of manufacture of electromagnetic induction apparatus.

In the manufacture of certain types of electromagnetic induction apparatus, it has proved to be advantageous to utilize preformed electrical conductive windings and to assemble the core to and upon those windings. It has further proved to be advantageous, particularly in conjunction with preformed windings, to form the core of wound, cold rolled steel strip.

In the general prior practice, a strip of cold rolled steel having a preferred direction of magnetization is wound upon a mandrel to form a spiral, and the wound core is then heat-treated to establish the permanent set of the metal, to relieve the internal strains and to improve the magnetic properties.

In one prior method of assembling the core to the electrical windings, the spiraled strip is rewound, in its entirety, into and on the preformed electrical winding.

To facilitate the assembly operation and to reduce the likelihood that the magnetic properties of the steel will be impaired due to working of the metal during assembly of the core to the conductive winding, it has further been suggested that the core strip be severed, during unwinding, into a plurality of sections, and thereafter assembled section-by-section upon the core, each section being placed in end-abutting relation with the preceding section.

It has been recognized, however, that such sectionalizing of the core tends to impair the magnetic qualities unless pains are taken to insure that the air gaps at the end abutments are adequately bridged by low-reluctance magnetic paths. Accordingly, it has further been suggested that the wound core be formed into sections which are plural turns in length, or that the sections be one or less turns in length, with the joints being staggered. The former method permits all of the sections to be formed into equal (e.g., 2, 2 /2, 3) turn-lengths and allows appreciable bridging of the butt joints, but requires the manipulation of plural turn-lengths of stock, retarding the speed of assembly and, again, leading to a danger of improper working of the stock subsequent to annealing. The latter method facilitates assembly, but requires that the core sections have substantially differing turn-lengths if the joints are to be staggered to an adequate degree to provide proper bridging or shunting of the air gaps.

The present invention relates to an improved method for constructing cores of the wound type. By virtue of the improved construction, the core can be formed of relatively short and easily handled sections, most of the sections can be of equal turn-lengths, and adequate bridging can be obtained at each of the end abutments. Further, the cross section of the core legs can be substantially constant.

In accordance with certain of the principles of the present invention, an electromagnetic induction apparatus is provided with an electrical winding structure and a magnetic core structure in linking interrelationship, with the core structure comprising a plurality of wound, pieced, interleaved-spiral magnetic strips. Each turn of each of the plural strips is separated from any other turn of that 3,466,744 Patented Sept. 16, 1969 strip by a turn of at least one other strip, and each strip is formed of a plurality of discrete individual portions, each of those portions being in end-abutting relation with the next preceding one of those portions. Each of the end abutments is magnetically bridged by a portion of another one of the strips, the distance between any end abutment of one of the spiral strips and the end abutment of the adjacent turn preferably being at least one-quarter of a turn-length so as to insure proper shunting of the highreluctance air gap with a low-reluctance path. In one embodiment of the invention, most of the end-abutment air gaps are shunted on both sides by portions of another spiraled strip or of other spiraled strips, while in one of the embodiments of the invention, bilateral multilayer bridging is provided, that is, each such end abutment is magnetically bridged by a plurality of portions of other strips on each side.

In the preferred practice, the end abutments of any one of the strips are substantially aligned radially of the core while the end abutments of a second spiraled strip are aligned along another and remotely spaced radius of the core structure. The radial alignment of the end abutments of each strip in this fashion permits the turn-lengths of the individual core sections to be constant, facilitating both manufacture and assembly.

To construct a core embodying the principles of the present invention, in the presently preferred method, a plurality of face-abutting strips of magnetic material are concurrently wound upon an arbor so as to form interleaved spirals in the nature of a bifilar winding. In the preferred procedure, the wound core is then heat-treated. Thereafter the intercoiled strips are unwound, without disturbing the permanent set and the plural strips are severed, as by shearing, at different spaced-apart locations during the unwinding so as to divide each of the strips into a plurality of strip portions. Desirably, but not imperatively, each of substantially all of the sections of each of the spirals is equal in turn-length to the others, so as to facilitate the shearing operation and the subsequent assembly operation. The core can advantageously be fabricated by making the core sections each one turn in length.

Subsequent to the shearing operation, the strips are appropriately stacked and are then assembled upon the electrical winding structure in their original, wound, interleaved spiral relationships. Since but relatively short lengths of stock are assembled to the winding structure, it is simpler to avoid excessive distortion of the strip during its insertion through the electrical winding structure.

A more complete understanding of the core structure, of the method of manufacturing of the core, and of the other principles of the present invention may be obtained from a consideration of the following detailed description of embodiments of the invention when read with reference to the accompanying drawings in which:

FIGURE 1 illustrates a partially completed electromagnetic induction apparatus embodying certain of the principles of the present invention;

FIG. 2 shows the core of the apparatus of FIG. 1 at one stage in its construction;

FIG. 3 illustrates the core of FIG. 2 at a later stage in its construction as well as shearing equipment for severing the strips into sections;

FIG. 4 is an enlarged view of the assembled core of FIG. 1;

FIG. 5 is a view of a modified form of assembled core; and

FIG. 6 is a view of the core of FIG. 5 at one stage in its construction along with a showing of shearing means for severing each of the plural strips of core material into sections.

In the electromagnetic induction apparatus represented in FIG. 1, a core structure is electromagnetically and mechanically linked with a pair of electrically conductive winding structures 12 and 14 each of which is performed prior to association with the core 10. It is to be understood that the showing of FIG. 1 is merely intended to illustrate one possible relationship between the core struc ture and the conductive winding structure and that the principles of the invention are applicable to arrangements in which conductive windings are associated with but one leg of the core, in which a plurality of winding means are associated with one or both core legs, and in which one preformed winding structure is common to two cores 10.

In the arrangement of PG. 1, the core 10 is formed with a generally rectangular window so as to establish the maximum space factor in relation to the cylindrical (here of generally rectangular cross-section) preformed winding structures.

The core 10 of FIG. 1 comprises a plurality of pieced,

interleaved-spiral magnetic strips, two such strips being employed in the embodiment of FIGS. 1 through 4 of the drawings. To construct such a core, two lengths of cold rolled strip steel of appropriate magnetic characteristics, width and thickness (normally about twelve thousandths of an inch) are brought into face-abutting relationship and wound upon a mandrel 16 (FIG. 2). While the mandrel 16 may be stationary and the two faceabutting strips wrapped around the mandrel, the more advantageous procedure is to align and face-abut the two strips 18 and 20, to secure, in any appropriate fashion, their respective ends 22 and 24 together and to one point upon the surface of the mandrel 16, and then to rotate the mandrel about the axis of the mandrel shaft 26, delivering the two strips approximately tangentially to the point of engagement with the mandrel. The incoming strips are or may be normally tensioned to a selected degree (with or without the application of radial pressure at the point of tangency) to provide the requisite tightness and/ or shape of core.

It has previously been recognized that in cores which are wound, unwound and assembled to the conductive winding structure, the creepage of the turns of the core from their initial, wound positions during assembly of the core to the conductive winding structure produces misalignment which renders the assembly of the core to its original form very diificult. To provide space to accommodate this creepage, spacers may be disposed between the turns during the winding operation. These spacers can be elements extending but a small portion of the turn-lengths, but it has been found to be preferable to uitilize string, fabric or other combustible materials which are coextensive with and lie parallel with the turns. Thus, one or more pieces of string or strips of combustible material can be placed on top of, between, or beneath (or any combination thereof) the two incoming aligned strips of material so that the combustible material is wound concurrently with the steel strips upon the mandrel 16.

As illustrated, a rectangular mandrel is employed in view of the assumed configuration of the preformed conductive winding means 12 and 14 (FIG. 1). Consequently, each turn is generally rectangular, having four straight leg portions and four right-angle turns, with each such turn being upon a radius.

Subsequent to the winding Operation as illustrated in FIG. 2, the core is heat-treated to anneal it and to destroy the combustible spacing material, if such was employed. Thereafter, the wound core is carefully unwound and the component spiraled strips are each severed into a plurality of sections, care being taken during this operation to avoid overstressing the annealed turns of the core. To perform this operation, the shaft 26' (FIG. 3) of the mandrel 16' (which may as a matter of manufacturing convenience but need not be the same elements as shaft 26 and mandrel 16 of FIG. 2) is rotatably supported so that the core 10 may be rotated about the axis of that shaft with the two strips of magnetic material 18 and 20 being drawn therefrom. The inner strip 18 is trained through a severing means 28 while the strip 20 constituting the outer spiral is trained through a severing means 30. Severing means 28 and 30 may be of any suitable well known type and it has been found to be satisfactory, with the subject construction, to employ shearing equipment, obviating the requirement of certain of the prior-art constructions for a sawing operation.

In this connection, it is to be understood that the term turn-length is intended to connote the length of any turn of the strip stock of the core, that is, one full turn of the strip even though the actual length of the strip required to complete one full turn will vary between the inner and the outer turn of the core due to the build-up Similarly, a half turn-length is the length of strip stock required at any point in the build-up to complete of winding of the core and two core lengths is the amount of strip stock, at any point in the build-up, required to complete 720 or two full turns of the core.

In the arrangement illustrated in FIG. 3, strip 18 is first severed at point 36 to form a portion or section 38 one-half turn-length long. Strip 18 is next severed at point 40 so as to produce a portion 42 one turn-length long. Strip 18 is thereafter sheared or otherwise severed each one turn-length. Strip 20 is first sheared at point 44 to form a portion 46 which is one turn-length long and is next sheared at point 48 to form a portion 50 which is also one turn-length long. Thereafter, strip 20 is cut into one turn-length sections. In the particular structure which is illustrated, the final cut of strip 18 will produce a onehalf-turn-length innermost section, while the final cut of strip 20 will prouce a one turn-length final section.

Following the severing operation, the portions are stacked in succession for convenience in storage and reassembly. Thereafter, the core portions are reassembled in their wound, interleaved spiral relationship about the conductive coil structure. The reassembled core is illustrated (with the conductive Winding structure omited for clarity) in the enlarged view of FIG. 4.

In the asssembly of the core 10 to the conductive winding structure, the innermost portion 52 of strip 18 is first placed inside the winding coil structure. The second innermost section 54 of strip 18 is then placed in endabutting relationship with portion 52, the end abutment 55 occurring at the top of the core structure in the illustration of FIG. 4. The innermost section 56 of strip 20 is then slipped between core portions 52 and 54, its innermost end 24 aligning with the innermost end 22 of the strip portion 52. Portion 56 extends to point 58, at the bottom leg of the core in the showing of FIG. 4, and the next step in the preferred assembly sequence is to bring section or portion 60 of the strip 20 into abutment with the portion 56 at junction 58. Thereafter, the next portion 62 of strip 18 is slipped between portions 56 and 60' of strip 20 with the inner end of strip 62 being brought into abutment with the outer end of strip 54 at point 64.

The building up of the core into its reassembled relationship proceeds in this fashion, terminating with the placing of the outer portion 46 of strip 20 over the outer portion 38 of the strip 18. The completely assembled core is then secured in position in any suitable, well known fashion.

While the end abutments of the strip 20 including abutments 44, 48 and 58 are shown to be radially aligned, and while the end abutments of the inner spiraled core strip 18, including abutments 55, 64, 40 and 36 are shown to be aligned along a radius spaced 180 from the line of the abutments of strip 20, it will be recognized that it is not imperative to the practice of all of the principles of the invention that the abutments of either strip be in alignment or that the 180 spacing be employed. However, as noted hereinbefore, it has been found to be advantageous from a number of standpoints to construct the core in this fashion.

It will be observed in the enlarged showing of FIG. 4 that except for the innermost abutment 55 and the outermost abutment 44, each end abutment or joint in the structure is bridged on both sides by a strip of magnetic material which extends a very substantial distance in both directions from the gap so as to insure that a low-reluctance bridge is established. Thus, in the illustrated arrangement, the bridging strips, in each case, are continuous for 180 in both lengthwise directions from the gap.

FIG. 5 of the drawings illustrates a reassembled core structure (with the conductive winding now shown) in which three strips of magnetic steel are utilized to form three interleaved spirals and FIG. 6 shows a step in the construction of the core of FIG. 5. In this modification, three strips of steel are brought into face-abutting relationship and wound upon a mandrel in the manner above discussed in connection with FIG. 2. After annealing, the three interleaved spiral windings are unwound and each strip is severed into a plurality of portions or sections during the unwinding operation, as illustrated in FIG. 6.

In the illustrated arrangement, the outer strip 70 is first severed at the one turn-length point 72 to form the portion 74 and is thereafter sheared each one turn-length. The intermediate strip 76 is first sheared at point 78 to define a one-quarter turn-length portion 80 and is thereafter cut into one turn lengths. The innermost strip 82 is first severed at point 84 to define a one-half turn-length portion 86 and is thereafter severed into one turn-length portions.

In reassembling the strip portions about the conductive winding structure, the innermost portion 94 is first placed within the conductive winding structure, this portion being one-half turn in length and terminating at abutment 96. Next, portion 98 of strip 82 is placed in end-abutting engagement with portion 94 at abutment 96. Core elements or portions 100 and 102, the innermost portions of strips 76 and 70, respectively, are then slipped between portions 94 and 98, their innermost ends being aligned with the innermost end of section 94. It will be observed that core portion 100 is three-quarters of a turn-length long (270") and hence terminates along the left-hand vertical leg of the core at junction 106 and that portion 102 is one turn-length long (360) and hence terminates at junction 108 along the bottom leg of the core.

Portion 110 of strip 82 is then placed in end-abutting relationship, at 106, with portion 100, and portion 112 of strip 76 is placed in end-abutting relationship, at 108, with portion 102. Succeeding strip portions are assembled in this fashion to complete the core.

In the core of FIG. 5, it will be observed that except for the innermost and outermost end abutments, each of the end abutments is bridged on both sides by a multiple layer of metal strip, each of the end junctions being representatively bridged by two layers of the strip steel at each side. Further, the bridging steel does not, in the disclosed arrangement, itself have a junction for at least 90 so that an excellent low-reluctance bridging or shunting path is provided for each of the air gaps which tend to exist at the end abutments, still further improving the magnetizing current characteristics in the vicinity of the joints.

The principles of the construction can be extended to four, five or n interleaved spiral strips. If the preferred practice above described is followed, the gaps in the four, five or n spiral paths will appear at four, five or n points along the magnetic path.

It is reiterated that it is not imperative to the practice of the principles of the invention that the end abutments in any one of the strips be aligned but that they may be staggered if desired, and it should further be noted that each of the strips illustrated in FIGS. 4 and 5 of the drawings may, if desired, actually be made up of plural component strip thicknesses. In that event, it is also not imperative that an equal number of metal thicknesses be employed to form each of the strips, that is, the number of constituent elements forming one of the spirals may be different than the number of metal thicknesses constituting another one of the spirals.

It will also be observed that the principle of concurrently winding a plurality of strips in interleaved spirals can also be applied to the manufacture of cores in which the strips are not pieced, possessing the advantage that the length of the material, with n interleaved spiral strips of a given thickness, which would have to be threaded through the winding structure to obtain a desired core thickness would be l/n of the total length which would be required if the entire core were formed of a single strip of the same thickness, as in the prior practice.

While it will be apparent that the embodiments of the invention herein disclosed are well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. The method of manufacturing an electromagnetic induction apparatus which comprises the steps of concurrently winding a plurality of face-abutting strips of magnetic material into interleaved spirals, annealing the magnetic material of said spirals, unwinding said spirals, severing a different initial length of material from each of said strips during unwinding to form an initial strip portion from each of the strips, thereafter severing each of said strips into strip portions of equal turn lengths during unwinding, and successively reassembling said strip portions into and on a preformed electrical winding structure into their wound, interleaved spiral relationship.

2. The method of claim 1 in which said reassembly step includes the substeps of slipping one end of one of the strip portions of one of said strips between two of the strip portions of another one of said strips.

3. The method of manufacturing an electromagnetic induction apparatus which comprises the steps of concurrently winding a plurality of face-abutting strips of magnetic material into interleaved spirals, annealing the magnetic material, unwinding said spirals, severing a different initial length of material from each of said strips during unwinding to form an initial strip poriton from each of the strips, thereafter severing each of said strips into strip portions of equal one-turn lengths during unwinding, and reassembling said strip portions into and on a preformed electrical winding structure in their wound, interleaved spiral relationship.

4. The method of manufacturing an electromagnetic induction apparatus which comprises the steps of concurrently winding a plurality of separate face-abutting strips of magnetic material into interleaved spirals, annealing the magnetic material, dividing each of said strips into a plurality of strip portions, and assembling said strip portions into and on a preformed electrical winding structure in the original, wound, interleaved spiral relationships of said strips by steps including the steps of slipping one end of one of the strip portions of one of said strips between two of the strip portions of another one of said strips.

5. The method of manufacturing an electromagnetic induction apparatus which comprises the steps of concurrently winding a plurality of separate face-abutting strips of magnetic material into interleaved spirals, annealing the magnetic material, dividing each of said strips into a plurality of strip portions, and assembling said strip portions into and on a preformed electrical winding structure in the original, wound, interleaved spiral relationships of said strips by steps including the steps of placing two strip portions of one of said strips about the electrical winding structure, and thereafter slipping one end of one 7 8 of the strip portions from the other one of said strips be- FOREIGN PATENTS tween said two previously placed strip portions. 521,125 5/1940 Great Britain References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, Pnmary Exarmner 3,008,222 11/1961 Steinmayer 29-15557 5 cHURcHAssistantExammer 2,689,396 9/1954 Viennean 29455.57

1,940,847 12/1933 Danziger -242 s6.1 2,927,366 3/19 0 Link 336-217 X 29-605, 242-56 3,122,821 3/1964 Beardsley et a]. 29l55.57 10 

1. THE METHOD OF MANUFACTURING AN ELECTROMAGNETIC INDUCTION APPARATUS WHICH COMPRISES THE STEPS OF CONCURRENTLY WINDING A PLURALITY OF FACE-ABUTTING STRIPS OF MAGNETIC MATERIAL INTO INTERLEAVED SPIRALS, ANNEALING THE MAGNETIC MATERIAL OF SAID SPIRALS, UNWINDING SAID SPIRALS, SERVING A DIFFERENT INITIAL LENGTH OF MATERIAL FROM EACH OF SAID STRIPS DURING UNWINDING TO FORM AN INITIAL STRIP PORTION FROM EACH OF THE STRIPS, THEREAFTER SEVERING EACH OF SAID STRIPS INTO STRIP PORTIONS OF EQUAL TURN LENGTHS DURING UNWINDING, AND SUCCESSIVELY REASSEMBLING SAID STRIP PORTIONS INTO AND ON A PREFORMED ELECTRICAL WINDING STRUCTURE INTO THEIR WOUND, INTERLEAVED SPIRAL RELATIONSHIP. 